The Response Of Soil Bacterial Communities And Larix Olgensis To Graphene And Graphene Oxide

With the wide application of nanomaterials in various fields,they will inevitably be released into the environment more and more.Graphene and graphene oxide are the basic structural units of carbon-nanomaterials and the support carriers of graphene-nanomaterials.It is important to study the ecological effects of both to scientifically evaluate the environmental risks of nanomaterials.Soil is the most important sink for nanomaterials,and soil bacterial communities are sensitive to environmental disturbances caused by the entry of exogenous materials.Current studies on the ecological effects of graphene-nanomaterials are mostly focused on fruit,vegetable and agricultural sites related to human daily life,but fewer studies have been conducted on natural habitats.We systematically investigated the response of rhizosphere bacterial community,nutrient content,and enzyme activity of dark brown forest soils,as well as the growth and physiological indicators of Larix olgensis seedlings under different concentrations of graphene and graphene oxide by indoor pot experiments.The ecological and environmental effects of graphene and graphene oxide on typical habitats in Northeast China were evaluated.The main findings are as follows:(1)The bacterial community of dark brown forest soils was sensitive to the addition of graphene and graphene oxide,and the Alpha and Beta diversity,composition and function of the community changed significantly,which is depended on the treatment concentrations.After the addition of graphene and graphene oxide,Alpha diversity analysis showed a significant increase in community richness,but the magnitude of the increase varied with different concentration treatments.Graphene(15.15 and 75.76 mg/kg)and graphene oxide(30.30 mg/kg)caused a decrease in community diversity.Beta diversity analysis showed that the structure of the community was significantly altered and varied with concentration.Community composition analysis showed that the species and relative abundance of bacteria changed.At the phylum level,six groups of bacteria,Proteobacteria,Acidobacteria,Chloroflexi,Actinobacteria,Verrucomicrobia and Nitrospirae,were the dominant phyla after addition.Proteobacteria and Acidobacteria were dominant.The average relative abundance size ranking of the remaining four phyla differed in the graphene and graphene oxide treatments.The predicted functional potential of the community showed that the intensity of metabolic function was mostly enhanced or not significantly changed after addition,and only 75.76 mg/kg graphene oxide treatment diminished the metabolic function intensity of bacteria.(2)The chemical properties and enzyme activities of dark brown forest soils varied after the addition of graphene and graphene oxide,which is depended on the treatment concentrations.Regarding chemical properties,the addition of both graphene and graphene oxide resulted in a significant decrease in p H,a decrease in organic matter(except for 30.30mg/kg graphene oxide),an increase in available phosphorus(except for 15.15 mg/kg graphene)and a decrease in available potassium with a significant difference between the specific concentration treatment and the control.With the increase of graphene and graphene oxide concentrations,both affected available phosphorus content of dark brown forest soils with the same trend,and for organic matter and available potassium,the differences were mainly in the high concentration treatments(75.76 and 151.52 mg/kg).Regarding enzyme activities,the addition of graphene and graphene oxide both reduced acid phosphatase activity and had no significant effect on dehydrogenase,but the effects on catalase and urease were different.There was no significant pattern in the trend of soil enzyme activity with increasing graphene and graphene oxide concentrations.Pearson correlation analysis showed significant correlations between some variables of dark brown forest soils properties and bacterial communities,but the correlation between p H and Verrucomicrobia,acid phosphatase activity and Chloroflexi had completely opposite results in the graphene and graphene oxide treatments.Redundancy analysis showed that p H,organic matter,and hydrolytic nitrogen were all critical factors on explaining the differences in soil bacterial communities,but the graphene and graphene oxide treatments differed in the order of importance.(3)The growth and physiological indicators of Larix olgensis seedlings changed after the addition of graphene and graphene oxide,which is depended on the treatment concentrations.After the addition of graphene and graphene oxide,the survival rate of seedlings decreased significantly,but the survival rate decreased significantly with the increase of graphene concentration and increased significantly with the increase of graphene oxide concentration.The root and stem dry weights of seedlings(except for 151.52 mg/kg graphene oxide)were reduced,but the specific concentration of graphene and graphene oxide resulted in an increase in leaf dry weight.The root,stem and leaf dry weights of seedlings showed a decreasing trend with increasing graphene concentration,but the stem and leaf dry weights of seedlings showed an increasing trend with increasing graphene oxide concentration.The root length and root surface area of seedlings were stressed.Graphene also inhibited the root volume of seedlings,but graphene oxide promoted the increase of root mean diameter to some extent.There were no significant changes on superoxide anion content,carotenoid,and chlorophyll content of seedling leaves,but specific concentration of graphene(151.52 mg/kg)increased the malondialdehyde content of leaves.As the concentration increased,there was a completely opposite trend between graphene and graphene oxide in carotenoids and chlorophyll content.